In Kondo insulator samarium hexaboride SmB6, strong correlation and band hybridization lead to an insulating gap and a diverging resistance at low temperature. The resistance divergence ends at about 5 Kelvin, a behavior recently demonstrated to arise from the surface conductance. However, questions remain whether and where a topological surface state exists. Quantum oscillations have not been observed to map the Fermi surface. We solve the problem by resolving the Landau Level quantization and Fermi surface topology using torque magnetometry. The observed Fermi surface suggests a two dimensional surface state on the (101) plane. Furthermore, the tracking of the Landau Levels in the infinite magnetic field limit points to -1/2, which indicates a 2D Dirac electronic state.The recent development of topological insulators is a triumph of single electron band theory [1][2][3][4][5][6][7][8] . It is interesting to understand whether similar exotic states of matter can arise once strong electronic interaction comes into play. Kondo insulators, a strongly-correlated heavyfermion system, offer a good playground for the exploration of this question. In a Kondo insulator 9,10 , the hybridization between itinerant electrons and localized orbitals opens a gap and makes the material insulating. Once the sample temperature is cold enough, the electronic structure in the strongly correlated system can be mapped to a rather simple electronic state that resembles a normal topological insulator 11 . As a result, in the ground state of the Kondo insulator there exists a bulk insulating state and a conductive surface state. In samarium hexaboride (SmB 6 ), the existence of the surface state has been suggested by recent experimental observations of the surface conductance as well as a map of the hybridization gap 12-14 . However, a direct observation of the Fermi surface has not yet been achieved by transport measurements in Kondo insulators. In this letter we report the observation of quantum oscillations in Kondo insulator SmB 6 using torque magnetometry. The observed Fermi surface is shown to be two-dimensional (2D) and arises from the crystalline (101) surface, and the Landau Level index plot shows a Berry phase contributed -1/2 factor in the infinite field limit, which indicates that this Fermi surface encloses Dirac points, a characteristic property of topological insulators.The direct observation of quantum oscillations is an essential step in understanding the electronic state of the bulk and surfaces of Kondo insulator. Wolgast et al. have argued strongly that the great robustness and certain other properties of the low T surface conductivity of SmB 6 are best understood as a consequence of having TI surface states 12 . Nonetheless there is yet no direct evidence for this interpretation of the surface conduction. Such evidence should come from microscopic measurements of the electronic structure, as has been accomplished for the weakly correlated TI materials, such as Bi 2 Se 3 , Bi 2 Te 3 , and graphene [15][16][17][18][19...

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The metastable α-phase GaO is an emerging material for developing solar-blind photodetectors and power electronic devices toward civil and military applications. Despite its superior physical properties, the high quality epitaxy of metastable phase α-GaO remains challenging. To this end, single crystalline α-GaO epilayers are achieved on nonpolar ZnO (112̅0) substrates for the first time and a high performance Au/α-GaO/ZnO isotype heterostructure-based Schottky barrier avalanche diode is demonstrated. The device exhibits self-powered functions with a dark current lower than 1 pA, a UV/visible rejection ratio of 10 and a detectivity of 9.66 × 10 cm Hz W. Dual responsivity bands with cutoff wavelengths at 255 and 375 nm are observed with their peak responsivities of 0.50 and 0.071 A W at -5 V, respectively. High photoconductive gain at low bias is governed by a barrier lowing effect at the Au/GaO and GaO/ZnO heterointerfaces. The device also allows avalanche multiplication processes initiated by pure electron and hole injections under different illumination conditions. High avalanche gains over 10 and a low ionization coefficient ratio of electrons and holes are yielded, leading to a total gain over 10 and a high responsivity of 1.10 × 10 A W. Such avalanche heterostructures with ultrahigh gains and bias-tunable UV detecting functionality hold promise for developing high performance solar-blind photodetectors.